In some locales, you want to do all of your internet use over one unlimited or high usage internet plan and handle SMS/calls over another carrier or plan. This

In some locales, you want to do all of your internet use over one unlimited or high usage internet plan and handle SMS/calls over another carrier or plan. This is appealing for business users and regular people alike in some places that have high tariffs, highly asymmetrical usage limits, or other uneven plan limits that don't align with how you use your mobile device. For example, I once had a lot of automated alerts sent by SMS to my phone for the early rollout of an IoT device I was working on. My regular unlimited voice and data plan was very cheap but only included a couple hundred SMS per month and I was going to blow past that during alpha testing, so I got a SIM from an MVNO with unlimited messaging for ~$5/mo and sent all the alerts to that number and had the company pay that bill, which was a nice way of isolating the expense as well. It's also great if you are an international jewel thief and need a second line for taunting the Interpol agents hot on your trail without having to add them to your friends & family plan.